Adaptive colour transform related signalling for both of cu level and tu level

ABSTRACT

There is included a method and apparatus comprising computer code configured to cause a processor or processors to perform obtaining video data, obtaining a coding unit (CU) block, determining whether a flag of the CU block is set to a predetermined flag condition, determining whether a tree type of the CU block is set to a predetermined tree type, determining whether to signal an adaptive color transform (ACT) flag based on any of whether the flag of the CU block is set to the predetermined flag condition and whether the tree type of the CU block is set to the predetermined tree type, and coding the video data based on a whether the ACT flag is signaled.

CROSS REFERENCE TO RELATED APPLICATION

This is a Continuation application of U.S. patent application Ser. No.17/319,328, filed May 13, 2021, which claims priority to provisionalapplication U.S. 63/037,170 filed on Jun. 10, 2020, the contents ofwhich are incorporated by reference herein in their entireties.

BACKGROUND 1. Field

The present disclosure relates to signaling of a coding unit (CU) levelenable flag and transform unit (TU) level luma. coded flag for the codedblock with an adaptive color transform (ACT) mode.

2. Description of Related Art

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) published theH.265/IEVC (High Efficiency Video Coding) standard in 2013 (version 1)2014 (version 2) 2015 (version 3) and 2016 (version 4). In 2015, thesetwo standard organizations jointly formed the JVET (Joint VideoExploration Team) to explore the potential of developing the next videocoding standard beyond HEVC In October 2017, they issued the Joint Callfor Proposals on Video Compression with Capability beyond HEVC (CfP). ByFeb. 15, 2018, total 22 CfP responses on standard dynamic range (SDR),12 CfP responses on high dynamic range (HDR), and 12 CfP responses on360 video categories were submitted, respectively. In April 2018, allreceived CfP responses were evaluated in the 122 MPEG/10th JVET meeting.As a result of this meeting, JVET formally launched the standardizationprocess of next-generation video coding beyond HEVC. The new standardwas named Versatile Video Coding (VVC), and JVET was renamed as JointVideo Expert Team.

However, there are technical problems such as if a coded CU block doesnot have a coefficient, then the ACT mode signaling may be redundant orthe CU with ACT mode should have one or more than one coefficient in thecoded CU block. For an inter block with ACT mode, if the cu_coded_flagshould be 1 to represent that the CU has at least one coefficient in atransform unit, then there is no corresponding constraint for the intraCU with ACT mode, and only the intra block with ACT mode should beinferred to 1 if the TU coded flag of chrominance channels are bothzero. Also, the cu_act_enabled_flag should be signaled twice based ondifferent prediction mode of the current CU block. As such, there aredescribed herein technical solutions to such problems for example.

SUMMARY

According to exemplary embodiments, there is included a method andapparatus comprising memory configured to store computer program codeand a processor or processors configured to access the computer programcode and operate as instructed by the computer program code. Thecomputer program code includes first obtaining code configured to causethe at least one processor to obtain video data, second obtaining codeconfigured to cause the at least one processor to obtain a coding unit(CU) block of the video data, first determining code configured to causethe at least one processor to determine whether a flag of the CU blockis set to a predetermined flag condition, second determining codeconfigured to cause the at least one processor to determine whether atree type of the CU block is set to a predetermined tree type, thirddetermining code configured to cause the at least one processor todetermine whether to signal an adaptive color transform (ACT) flag basedon any of whether the flag of the CU block is set to the predeterminedflag condition and whether the tree type of the CU block is set to thepredetermined tree type, and coding code configured to cause the atleast one processor to code the video data based on a whether the ACTflag is signaled.

According to exemplary embodiment, determining whether to signal the ACTflag is based on only whether the flag of the CU block is set to thepredetermined flag condition.

According to exemplary embodiment, determining whether to signal the ACTflag is based on both of whether the flag of the CU block is set to thepredetermined flag condition and whether the tree type of the CU blockis set to the predetermined tree type.

According to exemplary embodiment, the predetermined tree type indicatesa single tree type rather than a dual tree type.

According to exemplary embodiment, determining whether to signal anadaptive color transform (ACT) flag is implemented regardless of whethera prediction mode of the CU is an intra mode.

According to exemplary embodiment, the computer program code furtherincludes fourth determining code configured to cause the at least oneprocessor to determine whether transform unit (TU) coded flags are bothzero and whether the CU is coded with an ACT mode.

According to exemplary embodiment, the TU coded flags are flags ofchrominance channels.

According to exemplary embodiment, the computer program code furthercomprises fifth determining code configured to cause the at least oneprocessor to determine whether a TU coded flag of luminance is to beinferred to be 1 based on determining that the TU coded flags are bothzero and that the CU is coded with the ACT mode.

According to exemplary embodiments, determining the TU coded flag ofluminance is to be inferred to be 1 is implemented regardless of whethera prediction mode of the CU is an intra mode.

According to exemplary embodiments, coding the video data is furtherbased on determining whether the TU coded flag of luminance is to beinferred to be 1.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a simplified illustration of a schematic diagram in accordancewith embodiments.

FIG. 2 is a simplified illustration of a schematic diagram in accordancewith embodiments.

FIG. 3 is a simplified illustration of a schematic diagram in accordancewith embodiments.

FIG. 4 is a simplified illustration of a schematic diagram in accordancewith embodiments.

FIG. 5 is a simplified illustration of a diagram in accordance withembodiments.

FIG. 6 is a simplified illustration of a diagram in accordance withembodiments.

FIG. 7 is a simplified illustration of a diagram in accordance withembodiments.

FIG. 8 is a simplified illustration of a diagram in accordance withembodiments.

FIG. 9A is a simplified illustration of a diagram in accordance withembodiments.

FIG. 9B is a simplified illustration of a diagram in accordance withembodiments.

FIG. 10 is a simplified illustration of a flowchart in accordance withembodiments.

FIG. 11 is a simplified illustration of a flowchart in accordance withembodiments.

FIG. 12 a simplified illustration of a flowchart in accordance withembodiments.

FIG. 13 a simplified illustration of a diagram in accordance withembodiments.

FIG. 14 a simplified illustration of a diagram in accordance withembodiments.

FIG. 15 a simplified illustration of a schematic diagram in accordancewith embodiments.

DETAILED DESCRIPTION

The proposed features discussed below may be used separately or combinedin any order. Further, the embodiments may be implemented by processingcircuitry (e.g., one or more processors or one or more integratedcircuits). In one example, the one or more processors execute a programthat is stored in a non-transitory computer-readable medium.

FIG. 1 illustrates a simplified block diagram of a communication system100 according to an embodiment of the present disclosure. Thecommunication system 100 may include at least two terminals 102 and 103interconnected via a network 105. For unidirectional transmission ofdata, a first terminal 103 may code video data at a local location fortransmission to the other terminal 102 via the network 105. The secondterminal 102 may receive the coded video data of the other terminal fromthe network 105, decode the coded data and display the recovered videodata. Unidirectional data transmission may be common in media servingapplications and the like.

FIG. 1 illustrates a second pair of terminals 101 and 104 provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal 101 and 104 may code video data captured at a locallocation for transmission to the other terminal via the network 105.Each terminal 101 and 104 also may receive the coded video datatransmitted by the other terminal, may decode the coded data and maydisplay the recovered video data at a local display device.

In FIG. 1 , the terminals 101, 102, 103 and 104 may be illustrated asservers, personal computers and smart phones but the principles of thepresent disclosure are not so limited. Embodiments of the presentdisclosure find application with laptop computers, tablet computers,media players and/or dedicated video conferencing equipment. The network105 represents any number of networks that convey coded video data amongthe terminals 101, 102, 103 and 104, including for example wirelineand/or wireless communication networks. The communication network 105may exchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network 105may be immaterial to the operation of the present disclosure unlessexplained herein below.

FIG. 2 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and decoder in astreaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system 200 may include a capture subsystem 203, that caninclude a video source 201, for example a digital camera, creating, forexample, an uncompressed video sample stream 213. That sample stream 213may be emphasized as a high data volume when compared to encoded videobitstreams and can be processed by an encoder 202 coupled to the camera201. The encoder 202 can include hardware, software, or a combinationthereof to enable or implement aspects of the disclosed subject matteras described in more detail below. The encoded video bitstream 204,which may be emphasized as a lower data volume when compared to thesample stream, can be stored on a streaming server 205 for future use.One or more streaming clients 212 and 207 can access the streamingserver 205 to retrieve copies 208 and 206 of the encoded video bitstream204. A client 212 can include a video decoder 211 which decodes theincoming copy of the encoded video bitstream 208 and creates an outgoingvideo sample stream 210 that can be rendered on a display 209 or otherrendering device (not depicted). In some streaming systems, the videobitstreams 204, 206 and 208 can be encoded according to certain videocoding/compression standards. Examples of those standards are notedabove and described further herein.

FIG. 3 may be a functional block diagram of a video decoder 300according to an embodiment of the present invention.

A receiver 302 may receive one or more codec video sequences to bedecoded by the decoder 300; in the same or another embodiment, one codedvideo sequence at a time, where the decoding of each coded videosequence is independent from other coded video sequences. The codedvideo sequence may be received from a channel 301, which may be ahardware/software link to a storage device which stores the encodedvideo data. The receiver 302 may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver 302 may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory 303 may be coupled inbetween receiver 302 and entropy decoder/parser 304 (“parser”henceforth). When receiver 302 is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosychronous network, the buffer 303 may not be needed, or can besmall. For use on best effort packet networks such as the Internet, thebuffer 303 may be required, can be comparatively large and canadvantageously of adaptive size.

The video decoder 300 may include a parser 304 to reconstruct symbols313 from the entropy coded video sequence. Categories of those symbolsinclude information used to manage operation of the decoder 300, andpotentially information to control a rendering device such as a display312 that is not an integral part of the decoder but can be coupled toit. The control information for the rendering device(s) may be in theform of Supplementary Enhancement Information (SEI messages) or VideoUsability Information parameter set fragments (not depicted). The parser304 may parse/entropy-decode the coded video sequence received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow principles well known to aperson skilled in the art, including variable length coding, Huffmancoding, arithmetic coding with or without context sensitivity, and soforth. The parser 304 may extract from the coded video sequence, a setof subgroup parameters for at least one of the subgroups of pixels inthe video decoder, based upon at least one parameters corresponding tothe group. Subgroups can include Groups of Pictures (GOPs), pictures,tiles, slices, macroblocks, Coding Units (CUs), blocks, Transform Units(TUs), Prediction Units (PUs) and so forth. The entropy decoder/parsermay also extract from the coded video sequence information such astransform coefficients, quantizer parameter values, motion vectors, andso forth.

The parser 304 may perform entropy decoding/parsing operation on thevideo sequence received from the buffer 303, so to create symbols 313.The parser 304 may receive encoded data, and selectively decodeparticular symbols 313. Further, the parser 304 may determine whetherthe particular symbols 313 are to be provided to a Motion CompensationPrediction unit 306, a scaler/inverse transform unit 305, an IntraPrediction Unit 307, or a loop filter 311.

Reconstruction of the symbols 313 can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser 304. The flow of such subgroup control information between theparser 304 and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, decoder 300 can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit 305. Thescaler/inverse transform unit 305 receives quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) 313 from the parser 304. It can output blockscomprising sample values, that can be input into aggregator 310.

In some cases, the output samples of the scaler/inverse transform 305can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit 307. In some cases, the intra picture predictionunit 307 generates a block of the same size and shape of the block underreconstruction, using surrounding already reconstructed informationfetched from the current (partly reconstructed) picture 309. Theaggregator 310, in some cases, adds, on a per sample basis, theprediction information the intra prediction unit 307 has generated tothe output sample information as provided by the scaler/inversetransform unit 305.

In other cases, the output samples of the scaler/inverse transform unit305 can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit 306 canaccess reference picture memory 308 to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols 313 pertaining to the block, these samples can be addedby the aggregator 310 to the output of the scaler/inverse transform unit(in this case called the residual samples or residual signal) so togenerate output sample information. The addresses within the referencepicture memory form where the motion compensation unit fetchesprediction samples can be controlled by motion vectors, available to themotion compensation unit in the form of symbols 313 that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory when sub-sample exact motion vectors are in use, motionvector prediction mechanisms, and so forth.

The output samples of the aggregator 310 can be subject to various loopfiltering techniques in the loop filter unit 311. Video compressiontechnologies can include in-loop filter technologies that are controlledby parameters included in the coded video bitstream and made availableto the loop filter unit 311 as symbols 313 from the parser 304, but canalso be responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit 311 can be a sample stream that canbe output to the render device 312 as well as stored in the referencepicture memory 557 for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser 304), the current reference picture 309can become part of the reference picture buffer 308, and a fresh currentpicture memory can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder 300 may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also necessary for compliance can be that thecomplexity of the coded video sequence is within bounds as defined bythe level of the video compression technology or standard. In somecases, levels restrict the maximum picture size, maximum frame rate,maximum reconstruction sample rate (measured in, for example megasamplesper second), maximum reference picture size, and so on. Limits set bylevels can, in some cases, be further restricted through HypotheticalReference Decoder (HRD) specifications and metadata for HRD buffermanagement signaled in the coded video sequence.

In an embodiment, the receiver 302 may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder 300 to properly decode the data and/or to more accuratelyreconstruct the original video data. Additional data can be in the formof, for example, temporal, spatial, or signal-to-noise ratio (SNR)enhancement layers, redundant slices, redundant pictures, forward errorcorrection codes, and so on.

FIG. 4 may be a functional block diagram of a video encoder 400according to an embodiment of the present disclosure.

The encoder 400 may receive video samples from a video source 401 (thatis not part of the encoder) that may capture video image(s) to be codedby the encoder 400.

The video source 401 may provide the source video sequence to be codedby the encoder (303) in the form of a digital video sample stream thatcan be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, .. . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source 401 may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source 401 may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can comprise one or more samples depending on thesampling structure, color space, etc. in use. A person skilled in theart can readily understand the relationship between pixels and samples.The description below focuses on samples.

According to an embodiment, the encoder 400 may code and compress thepictures of the source video sequence into a coded video sequence 410 inreal time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofController 402. Controller controls other functional units as describedbelow and is functionally coupled to these units. The coupling is notdepicted for clarity. Parameters set by controller can include ratecontrol related parameters (picture skip, quantizer, lambda value ofrate-distortion optimization techniques, . . . ), picture size, group ofpictures (GOP) layout, maximum motion vector search range, and so forth.A person skilled in the art can readily identify other functions ofcontroller 402 as they may pertain to video encoder 400 optimized for acertain system design.

Some video encoders operate in what a person skilled in the art readilyrecognizes as a “coding loop.” As an oversimplified description, acoding loop can consist of the encoding part of an encoder 402 (“sourcecoder” henceforth) (responsible for creating symbols based on an inputpicture to be coded, and a reference picture(s)), and a (local) decoder406 embedded in the encoder 400 that reconstructs the symbols to createthe sample data that a (remote) decoder also would create (as anycompression between symbols and coded video bitstream is lossless in thevideo compression technologies considered in the disclosed subjectmatter). That reconstructed sample stream is input to the referencepicture memory 405. As the decoding of a symbol stream leads tobit-exact results independent of decoder location (local or remote), thereference picture buffer content is also bit exact between local encoderand remote encoder. In other words, the prediction part of an encoder“sees” as reference picture samples exactly the same sample values as adecoder would “see” when using prediction during decoding. Thisfundamental principle of reference picture synchronicity (and resultingdrift, if synchronicity cannot be maintained, for example because ofchannel errors) is well known to a person skilled in the art.

The operation of the “local” decoder 406 can be the same as of a“remote” decoder 300, which has already been described in detail abovein conjunction with FIG. 3 . Briefly referring also to FIG. 4 , however,as symbols are available and encoding and/or decoding of symbols to acoded video sequence by entropy coder 408 and parser 304 can belossless, the entropy decoding parts of decoder 300, including channel301, receiver 302, buffer 303, and parser 304 may not be fullyimplemented in local decoder 406.

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. The description of encodertechnologies can be abbreviated as they are the inverse of thecomprehensively described decoder technologies. Only in certain areas amore detail description is required and provided below.

As part of its operation, the source coder 403 may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine 407 codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder 406 may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder 403. Operations of the coding engine 407 may advantageouslybe lossy processes. When the coded video data may be decoded at a videodecoder (not shown in FIG. 4 ), the reconstructed video sequencetypically may be a replica of the source video sequence with someerrors. The local video decoder 406 replicates decoding processes thatmay be performed by the video decoder on reference frames and may causereconstructed reference frames to be stored in the reference picturecache 405. In this manner, the encoder 400 may store copies ofreconstructed reference frames locally that have common content as thereconstructed reference frames that will be obtained by a far-end videodecoder (absent transmission errors).

The predictor 404 may perform prediction searches for the coding engine407. That is, for a new frame to be coded, the predictor 404 may searchthe reference picture memory 405 for sample data (as candidate referencepixel blocks) or certain metadata such as reference picture motionvectors, block shapes, and so on, that may serve as an appropriateprediction reference for the new pictures. The predictor 404 may operateon a sample block-by-pixel block basis to find appropriate predictionreferences. In some cases, as determined by search results obtained bythe predictor 404, an input picture may have prediction references drawnfrom multiple reference pictures stored in the reference picture memory405.

The controller 402 may manage coding operations of the video coder 403,including, for example, setting of parameters and subgroup parametersused for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder 408. The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter 409 may buffer the coded video sequence(s) as created bythe entropy coder 408 to prepare it for transmission via a communicationchannel 411, which may be a hardware/software link to a storage devicewhich would store the encoded video data. The transmitter 409 may mergecoded video data from the video coder 403 with other data to betransmitted, for example, coded audio data and/or ancillary data streams(sources not shown).

The controller 402 may manage operation of the encoder 400. Duringcoding, the controller 405 may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as one of the following frame types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh Pictures. A personskilled in the art is aware of those variants of I pictures and theirrespective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder 400 may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder 400 may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter 409 may transmit additional data withthe encoded video. The source coder 403 may include such data as part ofthe coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

FIG. 5 illustrates intra prediction modes used in HEVC and JEM. Tocapture the arbitrary edge directions presented in natural video, thenumber of directional intra modes is extended from 33, as used in HEVC,to 65. The additional directional modes in JEM on top of HEVC aredepicted as dotted arrows in FIG. 1(b), and the planar and DC modesremain the same. These denser directional intra prediction modes applyfor all block sizes and for both luma and chroma intra predictions. Asshown in FIG. 5 , the directional intra prediction modes as identifiedby dotted arrows, which is associated with an odd intra prediction modeindex, are called odd intra prediction modes. The directional intraprediction modes as identified by solid arrows, which are associatedwith an even intra prediction mode index, are called even intraprediction modes. In this document, the directional intra predictionmodes, as indicated by solid or dotted arrows in FIG. 5 are alsoreferred as angular modes.

In JEM, a total of 67 intra prediction modes are used for luma intraprediction. To code an intra mode, a most probable mode (MPM) list ofsize 6 is built based on the intra modes of the neighboring blocks. Ifintra mode is not from the MPM list, a flag is signaled to indicatewhether intra mode belongs to the selected modes. In JEM-3.0, there are16 selected modes, which are chosen uniformly as every fourth angularmode. In JVET-D0114 and JVET-G0060, 16 secondary MPMs are derived toreplace the uniformly selected modes.

FIG. 6 illustrates N reference tiers exploited for intra directionalmodes. There is a block unit 611, a segment A 601, a segment B 602, asegment C 603, a segment D 604, a segment E 605, a segment F 606, afirst reference tier 610, a second reference tier 609, a third referencetier 608 and a fourth reference tier 607.

In both HEVC and JEM, as well as some other standards such as H.264/AVC,the reference samples used for predicting the current block arerestricted to a nearest reference line (row or column). In the method ofmultiple reference line intra prediction, the number of candidatereference lines (row or columns) are increased from one (i.e. thenearest) to N for the intra directional modes, where N is an integergreater than or equal to one. FIG. 2 takes 4×4 prediction unit (PU) asan example to show the concept of the multiple line intra directionalprediction method. An intra-directional mode could arbitrarily chooseone of N reference tiers to generate the predictors. In other words, thepredictor p(x,y) is generated from one of the reference samples S1, S2,. . . , and SN. A flag is signaled to indicate which reference tier ischosen for an intra-directional mode. If N is set as 1, the intradirectional prediction method is the same as the traditional method inJEM 2.0. In FIG. 6 , the reference lines 610, 609, 608 and 607 arecomposed of six segments 601, 602, 603, 604, 605 and 606 together withthe top-left reference sample. In this document, a reference tier isalso called a reference line. The coordinate of the top-left pixelwithin current block unit is (0,0) and the top left pixel in the 1streference line is (−1,−1).

In JEM, for the luma component, the neighboring samples used for intraprediction sample generations are filtered before the generationprocess. The filtering is controlled by the given intra prediction modeand transform block size. If the intra prediction mode is DC or thetransform block size is equal to 4×4, neighboring samples are notfiltered. If the distance between the given intra prediction mode andvertical mode (or horizontal mode) is larger than predefined threshold,the filtering process is enabled. For neighboring sample filtering, [1,2, 1] filter and bi-linear filters are used.

A position dependent intra prediction combination (PDPC) method is anintra prediction method which invokes a combination of the un-filteredboundary reference samples and HEVC style intra prediction with filteredboundary reference samples. Each prediction sample pred[x][y] located at(x,y) is calculated as follows:

pred[x][y]=(wL*R _(−1,y) +wT*R _(x,−1) +wTL*R_(−1,−1)+(64−wL−wT−wTL)*pred[x][y]+32)>>6  (Eq. 1)

-   -   where R_(x,−1), R_(−1,y) represent the unfiltered reference        samples located at top and left of current sample (x,y),        respectively, and R_(−1,−1) represents the unfiltered reference        sample located at the top-left corner of the current block. The        weightings are calculated as below,

wT=32>>((y<<1)>>shift)  (Eq. 2)

wL=32>>((x<<1)>>shift)  (Eq. 3)

wTL=−(wL>>4)−(wT>>4)  (Eq. 4)

shift=(log 2(width)+log 2(height)+2)>>2  (Eq. 5).

FIG. 7 illustrates a diagram 700 in which DC mode PDPC weights (wL, wT,wTL) for (0, 0) and (1, 0) positions inside one 4×4 block. If PDPC isapplied to DC, planar, horizontal, and vertical intra modes, additionalboundary filters are not needed, such as the HEVC DC mode boundaryfilter or horizontal/vertical mode edge filters. FIG. 7 illustrates thedefinition of reference samples Rx,−1, R−1,y and R−1,−1 for PDPC appliedto the top-right diagonal mode. The prediction sample pred(x′, y′) islocated at (x′, y′) within the prediction block. The coordinate x of thereference sample Rx,−1 is given by: x=x′+y′+1, and the coordinate y ofthe reference sample R−1,y is similarly given by: y=x′+y′+1.

FIG. 8 illustrates a Local Illumination Compensation (LIC) diagram 800and is based on a linear model for illumination changes, using a scalingfactor a and an offset b. And it is enabled or disabled adaptively foreach inter-mode coded coding unit (CU).

When LIC applies for a CU, a least square error method is employed toderive the parameters a and b by using the neighboring samples of thecurrent CU and their corresponding reference samples. More specifically,as illustrated in FIG. 8 , the subsampled (2:1 subsampling) neighboringsamples of the CU and the corresponding samples (identified by motioninformation of the current CU or sub-CU) in the reference picture areused. The IC parameters are derived and applied for each predictiondirection separately.

When a CU is coded with merge mode, the LIC flag is copied fromneighboring blocks, in a way similar to motion information copy in mergemode; otherwise, an LIC flag is signaled for the CU to indicate whetherLIC applies or not.

FIG. 9A illustrates intra prediction modes 900 used in HEVC. In HEVC,there are total 35 intra prediction modes, among which mode 10 ishorizontal mode, mode 26 is vertical mode, and mode 2, mode 18 and mode34 are diagonal modes. The intra prediction modes are signaled by threemost probable modes (MPMs) and 32 remaining modes.

FIG. 9B illustrates, in embodiments of VVC, there are total 87 intraprediction modes where mode 18 is horizontal mode, mode 50 is verticalmode, and mode 2, mode 34 and mode 66 are diagonal modes. Modes −1˜−10and Modes 67˜76 are called Wide-Angle Intra Prediction (WAIP) modes.

The prediction sample pred(x,y) located at position (x,y) is predictedusing an intra prediction mode (DC, planar, angular) and a linearcombination of reference samples according to the PDPC expression:

pred(x,y)=(wL×R−1,y+wT×Rx,−1−wTL×R−1,−1+(64−wL−wT+wTL)×pred(x,y)+32)>>6  (6)

-   -   where Rx,−1, R−1,y represent the reference samples located at        the top and left of current sample (x,y), respectively, and        R−1,−1 represents the reference sample located at the top-left        corner of the current block.

For the DC mode the weights are calculated as follows for a block withdimensions width and height:

wT=32>>((y<<1)>>nScale),wL=32>>((x<<1)>>nScale),wTL=(wL>>4)+(wT>>4),  (7)

-   -   with nScale=(log 2(width)−2+log 2(height)−2+2)>>2, where wT        denotes the weighting factor for the reference sample located in        the above reference line with the same horizontal coordinate, wL        denotes the weighting factor for the reference sample located in        the left reference line with the same vertical coordinate, and        wTL denotes the weighting factor for the top-left reference        sample of the current block, nScale specifies how fast weighting        factors decrease along the axis (wL decreasing from left to        right or wT decreasing from top to bottom), namely weighting        factor decrement rate, and it is the same along x-axis (from        left to right) and y-axis (from top to bottom) in current        design. And 32 denotes the initial weighting factors for the        neighboring samples, and the initial weighting factor is also        the top (left or top-left) weightings assigned to top-left        sample in current CB, and the weighting factors of neighboring        samples in PDPC process should be equal to or less than this        initial weighting factor.

For planar mode wTL=0, while for horizontal mode wTL=wT and for verticalmode wTL=wL. The PDPC weights can be calculated with adds and shiftsonly. The value of pred(x,y) can be computed in a single step using Eq.1.

Herein the proposed methods may be used separately or combined in anyorder. Further, each of the methods (or embodiments), encoder, anddecoder may be implemented by processing circuitry (e.g., one or moreprocessors or one or more integrated circuits). In one example, the oneor more processors execute a program that is stored in a non-transitorycomputer-readable medium. In the following, the term block may beinterpreted as a prediction block, a coding block, or a coding unit,i.e. CU.

FIG. 10 illustrates exemplary embodiments of a flowchart 1000 such thatat S100, data may be received such that at S101 it may be determinedwhether to implement processing for a unit such as a coding unit and ora transform unit. If so, at S102, then it may be determined if thecoding unit is including an intra mode prediction. If so, then at S103,it may be determined if the coding unit is including a flag indicatingwhether SPS ACT is enabled, and if there is such indication in suchflag, at S104, then it may also be determined if a tree type for thecoding unit is a single tree type or not. According to exemplaryembodiments, an sps_act_enabled_flag equal to 1 specifies that adaptivecolor transform may be used and the cu_act_enabled_flag may be presentin the coding unit syntax.; an sps_act_enabled_flag equal to 0 mayspecify that adaptive color transform may not be used andcu_act_enabled_flag may not be present in the coding unit syntax; andwhen sps_act_enabled_flag is not present, may be inferred to be equal to0.

If it is determined at S102, S103, and S104 that the intra mode, theflag indicating enablement of the SPS ACT, and that a tree is a singletree type, then at S105, the processing may set a flag indicating thatACT is enabled in that coding unit at S105. According to exemplaryembodiments, a cu_act_enabled_flag equal to 1 may specify that theresiduals of the current coding unit are coded in YCgCo color space; acu_act_enabled_flag equal to 0 may specify that the residuals of thecurrent coding unit are coded in original color space; and when acu_act_enabled_flag is not present, it may be inferred to be equal to 0.As such, based on such syntax, an inter block could be encoded with ACTmode if the cu_coded_flag is 1 which may be interpreted as meaning thatACT mode could be enabled for inter block if there is more than onecoefficient in the current CU.

Then at S106 further processing discussed herein may be implemented aswell as looping to S101 described above. Alternatively at S102, if it isdetermined that the mode is not set for intra, and/or at S103 if it isdetermined that an sps_act_enabled flag does not include such enabledindication, then at S107, it may be determined if there is an indicationregarding a PLT prediction flag, and if not, then at S108 adetermination of a value of a general_merge_flag. If such values atS102, S107, and S108 are set as discussed below, then the processing mayset, at S109, a cu_coded_flag, whereafter at S110, or from S107 andS108, if there is currently set such cu_coded_flag, at S111 it may bedetermined if the coding unit is including a flag indicating whether SPSACT is enabled, and if there is such indication in such flag, at S112,then it may be determined if an intra mode is now indicated, and if not,the processing may proceed at S104 as noted above.

FIG. 11 illustrates exemplary embodiments of a flowchart 1100 such thatat such that at S100, data may be received such that at S101 it may bedetermined whether to implement processing for a coding unit and or atransform unit. For example, regardless of at S201 or at S202 if thereis a current CU in a prediction mode Intra (S201) or not (S202), theprocessing may proceed at S203 to determine when a TU coded flag ofchrominance channels are both zero. If so, at S203, then by theillustrated Y′, then such determination at S203 may be sufficient toproceed to S204 in inferring that a TU coded flag of luminance should beinferred to 1, and therefore, such inference may be made regardless ofwhether the current prediction mode of a current CU block is MODE_INTRAor not. Further, it may also be, in addition to such positivedetermination at S203, that the TU coded flag of chrominance channelsare both zero, whether also the current CU is coded with an ACT mode,and if so, then the proceed may then proceed to S204 rather thanstraightaway after S203. Nonetheless, at S204 thereafter and withnegative determinations at S203, the processing may proceed as describedat any of S100 and S106 as described above. According to embodiments,for a coding block with ACT on, a tu_y_coded_flag may not be signaled inthe bitstream and should be inferred to 1 when the TU coded flag ofchrominance channels are both zero. Further, a cu_act_enabled_flagsignal may be signaled according to such exemplary embodiments withoutthe checking of the prediction mode of current CU block (S201 and orS202) such that in embodiments for example, for a coding unit, only twoconditions, sps_act_enabled_flag and treeType is SINGLE_TREE, for thesignaling of the cu_act_enabled_flag may be checked and therefore theadvantage of avoiding a conditionally signaling of thecu_act_enabled_flag twice based on the prediction mode may be achievedas described below and also shown in FIG. 12 for example.

For embodiments with a tu_y_coded_flag of a current CU block that mayintentionally not be signaled when the TU coded flags of both chromachannels are 0 and an ACT flag is 1, see Table 1, where, among otherthings, a . . . CuPredMode[chType][x0][y0]==MODE_INTRA “&&!cu_act_enabled_flag” . . . is included with signaling in TU level forACT:

TABLE 1 Descriptor transform_unit( x0, y0, tbWidth, tbHeight, treeType,subTuIndex, chType ) {  ...  if( ( treeType = = SINGLE_TREE | | treeType= = DUAL_TREE_CHROMA ) &&    ChromaArrayType != 0 && (IntraSubPartitionsSplitType = = ISP_NO_SPLIT &&    ( ( subTuIndex = = 0&& cu_sbt_pos_flag ) | |    ( subTuIndex = = 1 && !cu_sbt_pos_flag ) ) )) | |    ( IntraSubPartitionsSplitType != ISP_NO_SPLIT &&    (subTuIndex = = NumIntraSubPartitions − 1 ) ) ) {   tu_cb_coded_flag[ xC][ yC ] ae(v)   tu_cr_coded_flag[ xC ][ yC ] ae(v)  }  if( treeType = =SINGLE_TREE | | treeType = = DUAL_TREE_LUMA) {   if( (IntraSubPartitionsSplitType = = ISP_NO_SPLIT && !( cu_sbt_flag &&     (( subTuIndex = = 0 && cu_sbt_pos_flag ) | |     ( subTuIndex = = 1 &&!cu_sbt_pos_flag ) ) ) &&     ( ( CuPredMode[ chType ][ x0 ][ y0 ] = =MODE_INTRA && !cu_act_enabled_flag ) | |     ( chromaAvailable && (tu_cb_coded_flag[ xC ] [ yC ] | |     tu_cr_coded_flag[ xC ][ yC ] ) ) ||     CbWidth[ chType ][ x0 ][ y0 ] > MaxTbSizeY | |     CbHeight[chType ][ x0 ][ y0 ] > MaxTbSizeY ) ) | |    (IntraSubPartitionsSplitType != ISP_NO_SPLIT &&     ( subTuIndex <NumIntraSubPartitions − 1 | | !InferTuCbfLuma ) ) )    tu_y_coded_flag[x0 ][ y0 ] ae(v)   if(IntraSubPartitionsSplitType != ISP_NO_SPLIT )   InferTuCbfLuma = InferTuCbfLuma && !tu_y_coded flag[ x0 ][y0 ]  } if( ( CbWidth chType ][ x0 ][ y0 ] > 64 | | CbHeight chType ][ x0 ][ y0] > 64 | |  tu_y_coded_flag[ x0 ][ y0 ] | | ( chromaAvailable && (tu_cb_coded_flag[ xC ][ yC ] | |    tu_cr_coded_flag[ xC ][ yC ] ) ) &&treeType != DUAL_TREE_CHROMA &&    pps_cu_qp_delta_enabled_flag &&!IsCuQpDeltaCoded ) {   cu_qp_delta_abs ae(v)   if( cu_qp_delta_abs )   cu_qp_delta_sign_flag ae(v) }

According to embodiments with a condition of cu_act_enabled_flagsignaling for the current CU block including sps_act_enabled_flag andtree type only according to exemplary embodiments as shown by Table 2with respect to cu_act_enabled_flag signaling in CU level for ACT:

TABLE 2 Descriptor coding_unit( x0, y0, cbWidth, cbHeight, cqtDepth,treeType, modeType ) {  chType = treeType = = DUAL_TREE_CHROMA ? 1 : 0 ...  ifsps_act_enabled_flag &&   treeType = = SINGLE_TREE )  cu_act_enabled_flag ae(v)  ...  if( CuPredMode[ chType ][ x0 ][ y0 ]!= MODE_INTRA && !pred_mode_plt_flag &&   general_merge_flag[ x0 ][ y0 ]= = 0 )   cu_coded_flag_cu_act_enabled_flag ae(v)  if( cu_coded_flag ) {  ...   LfnstDcOnly = 1 ae(v)   ...  }

For example, FIG. 12 illustrates exemplary embodiments of a flowchart1200 such that at S100, data may be received such that at S301 it may bedetermined whether to implement processing for a coding unit and or atransform unit If so, at S302, it may be determined if the coding unitis including a flag indicating whether SPS ACT is enabled, and if thereis such indication in such flag, at S304, then it may also be determinedif a tree type for the coding unit is a single tree type or not.According to such exemplary embodiments, an sps_act_enabled_flag equalto 1 specifies that adaptive color transform may be used and thecu_act_enabled_flag may be present in the coding unit syntax.; ansps_act_enabled_flag equal to 0 speifies that adaptive color transformmay not used and cu_act_enabled_flag may not be present in the codingunit syntax; and when sps_act_enabled_flag is not present, may beinferred to be equal to 0.

If it is determined at S302 and S304 that the flag indicates enablementof the SPS ACT, and that a tree is a single tree type, then at S305, theprocessing may set a flag indicating that ACT is enabled in that codingunit at S305. According to exemplary embodiments, a cu_act_enabled_flagequal to 1 may specify that the residuals of the current coding unit arecoded in YCgCo color space; a cu_act_enabled_flag equal to 0 may specifythat the residuals of the current coding unit are coded in originalcolor space; and when a cu_act_enabled_flag is not present, it may beinferred to be equal to 0. As such, based on such syntax, an inter blockcould be encoded with ACT mode if the cu_coded_flag is 1 which may beinterpreted as meaning that ACT mode could be enabled for inter block ifthere is more than one coefficient in the current CU.

Then at S106 further processing discussed herein may be implemented aswell as looping to S301 described above. Alternatively at S302, if it isdetermined that an sps_act_enabled flag does not include such enabledindication, then at S307, it may be determined if there is an indicationregarding a PLT prediction flag, and if not, then at S808 adetermination of a value of a general_merge_flag. If such values atS302, S307, and S308 are set accordingly as shown in FIG. 8 , then theprocessing may set, at S309, a cu_coded_flag described above.

Accordingly, such embodiments solve various technical problems when forexample, if the coded CU block doesn't have any coefficient, the ACTmode should not be signaled anymore whereby accordingly the CU with theACT mode should have one or more than one coefficient in the coded CUblock, and for the inter block with ACT mode, the cu_coded_flag shouldbe 1 to represent that the CU has at least one coefficient in transformunit thereby solving absent constraints for the intra CU with ACT mode.

Such features represent advantageous coding tools such as for RGBvideos. For example, see the illustration 1300 in FIG. 13 in which thereis illustrated an encoding flow 1301 and decoding flow 1302 whereinthere is illustrated in-loop ACT adopted into screen coding models (SCM)(such as a software test model of screen content coding extension ofHEVC), where ACT is illustrated as operated in a residue domain, and aCU-level flag may be signaled to indicate a usage of the color-spacetransform. Such color transform used in SCM may be, according toexemplary embodiments, as follows:

$\begin{matrix}{{{Forward}{transform}{:\begin{bmatrix}Y \\C_{g} \\C_{o}\end{bmatrix}}} = {{\frac{1}{4}\begin{bmatrix}1 & 2 & 1 \\{- 1} & 2 & {- 1} \\2 & 0 & {- 2}\end{bmatrix}} \times \begin{bmatrix}R \\G \\B\end{bmatrix}}} & (8)\end{matrix}$ $\begin{matrix}{{{Backward}{transform}{:\begin{bmatrix}R \\G \\B\end{bmatrix}}} = {\begin{bmatrix}1 & {- 1} & 1 \\1 & 1 & 0 \\1 & {- 1} & {- 1}\end{bmatrix} \times \begin{bmatrix}Y \\C_{g} \\C_{o}\end{bmatrix}}} & (9)\end{matrix}$

Further, in the illustration 1400 in FIG. 14 there is illustrated adecoding process according to exemplary embodiments with the ACT suchthat, in view of the above-described embodiments and flowcharts,included the ACT tool in HEVC into the VVC framework to enhance theefficiency of video coding whereby decoding with the ACT may be soapplied. As in FIG. 14 , it is shown in the illustration 1400 that acolor space conversion may be carried out in a residual domain, andspecifically, an additional decoding module, namely an inverse ACT, maybe introduced, such as after an inverse transform so as to convertresiduals from a YCgCo domain back to an original domain. Accordingly,viewing the above described FIGS. 10-12 among the other disclosures,advantages are achieved over features in the VVC, when the maximumtransform size is not smaller than the width or height of one codingunit (CU), one CU leaf node may also used as the unit of transformprocessing, and therefore, in embodiments herein, an ACT flag may besignaled for one CU to select the color space for coding its residuals,and following such HEVC ACT design, for inter and intra-block copy (IBC)CUs, the ACT may be only enabled when there is at least one non-zerocoefficient in the CU, and for intra CUs, the ACT may only be enabledwhen chroma components select the same intra prediction mode of lumacomponent, i.e., a DM mode, thereby advantageously at least avoidingsuch unnecessary or otherwise redundant signaling according to exemplaryembodiments.

According to exemplary embodiments, core transforms used for the colorspace conversions may be with respect to the following forward andinverse YCgCo color transform matrices, as described as follows, asapplied. For example:

$\begin{matrix}{{{{forward}{transform}}{:\begin{bmatrix}C_{0}^{\prime} \\C_{1}^{\prime} \\C_{2}^{\prime}\end{bmatrix}}} = {{\begin{bmatrix}2 & 1 & 1 \\2 & {- 1} & {- 1} \\0 & {- 2} & 2\end{bmatrix}\begin{bmatrix}C_{0} \\C_{1} \\C_{2}\end{bmatrix}}/4}} & (10)\end{matrix}$ ${{inversed}{transform}{:\begin{bmatrix}C_{0} \\C_{1} \\C_{2}\end{bmatrix}}} = {\begin{bmatrix}1 & 1 & 0 \\1 & {- 1} & {- 1} \\1 & {- 1} & 1\end{bmatrix}\begin{bmatrix}C_{0}^{\prime} \\C_{1}^{\prime} \\C_{2}^{\prime}\end{bmatrix}}$

Additionally, to compensate the dynamic range change of residualssignals before and after color transform, the QP adjustments, such as of(−5,−5,−3) may be, applied to the transform residuals. On the otherhand, as shown in (1), forward and inverse color transforms may need toaccess the residuals of all three components. Correspondingly, inembodiments of the present application, the technical improvement ofallowing for the ACT to be disabled in the following scenarios where notall residuals of three components are available. For example, viewingFIGS. 10-12 and descriptions, there is a separate-tree partition casesuch that when a separate-tree is applied, luma and chroma samplesinside one CTU are partitioned by different structures, which may resultin that the CUs in the luma-tree only contains luma component and theCUs in the chroma-tree only contains two chroma components and alsothere is an intra sub-partition prediction (ISP) case in which the ISPsub-partition may only be applied to luma while chroma signals are codedwithout splitting, and in such ISP design, except the last ISPsub-partitions, the other sub-partitions only contain luma componentaccording to embodiments.

Accordingly, there may be such CU level signaling of ACT where CU levelACT related signaling may be included according to coding syntax tables,such also as the above tables and/or Table 3:

TABLE 3 Descriptor coding_unit( x0, y0, cbWidth, cbHeight, cqtDepth,treeType, modeType ) {  chType = treeType = = DUAL_TREE_CHROMA ? 1 : 0 ...  if( CuPredMode[ chType ][ x0 ][ y0 ] = = MODE_INTRA &&sps_act_enabled_flag &&   treeType = = SINGLE_TREE )   cu_act_enabled_flag ae(v)  ...  if( CuPredMode[ chType ][ x0 ][ y0 ]!= MODE_INTRA && !pred_mode_plt_flag &&   general_merge_flag[ x0 ][ y0 ]= = 0 )   cu_coded_flag ae(v)  if( cu_coded_flag ) {   ...   if(sps_act_enabled_flag && CuPredMode[ chType ] [ x0 ][ y0 ] != MODE_INTRA&&    treeType = = SINGLE_TREE )     cu_act_enabled_flag ae(v)  LfnstDcOnly = 1 ae(v)   ...  }

In embodiments, an sps_act_enabled_flag equal to 1 may specify that anadaptive color transform may be used and the cu_act_eabled_flag may bepresent in the coding unit syntax, and sps_act_enabled_flag equal to 0may specify that an adaptive color transform may not be used and that acu_act_enabled_flag may not be present in the coding unit syntax, andwhen an sps_act_enabled_flag is not present, it may be inferred to beequal to 0. In embodiments, a cu_act_enabled_flag equal to 1 may specifythat the residuals of the current coding unit are coded in YCgCo colorspace, a cu_act_enabled_flag equal to 0 may specify that the residualsof the current coding unit are coded in original color space, and when acu_act_enabled_flag is not present, it may be inferred to be equal to 0.According to exemplary embodiments, based on the above syntax, an interblock may be encoded with ACT mode if the cu_coded_flag is 1 and therebyan ACT mode may be enabled for an inter block in a case such as if thereis more than one coefficient in a current CU.

Further, syntax with respect to a TU level luma coded flag signaling foran ACT block, such as a TU coded flag for three color channels, may beincluded according to a following transform unit syntax table, Table 4:

TABLE 4 Descriptor transform_unit( x0, y0, tbWidth, tbHeight, treeType,subTuIndex, chType ) {  ...  if( (treeType = = SINGLE_TREE | | treeType= = DUAL_TREE_CHROMA ) &&    ChromaArrayType != 0 &&(IntraSubPartitionsSplitType = = ISP_NO_SPLIT &&    ( ( subTuIndex = = 0&& cu_sbt_pos_flag ) | |    ( subTuIndex = = 1 && !cu_sbt_pos_flag ) ) )) | |    ( IntraSubPartitionsSplitType != ISP_NO_SPLIT &&    (subTuIndex = = NumIntraSubPartitions − 1 ) ) ) {   tu_cb_coded_flag[ xC][ yC ] ae(v)   tu_cr_coded_flag[ xC ][ yC ] ae(v)  }  if( treeType = =SINGLE_TREE | | treeType = = DUAL_TREE_LUMA ) {   if( (IntraSubPartitionsSplitType = = ISP_NO_SPLIT && !( cu_sbt_flag &&     (( subTuIndex = = 0 && cu_sbt_pos_flag ) | |     ( subTuIndex = = 1 &&!cu_sbt_pos_flag ) ) ) && | |     ( CuPredMode[ chType ][ x0 ][ y0 ] = =MODE_INTRA | |     ( chromaAvailable && ( tu_cb_coded_flag[ xC ] [ yC ]| |     tu_er_coded_flag[ xC ] [ yC ] ) )     CbWidth[ chType ] [ x0 ][y0 ] > MaxTbSizeY | |     CbHeight[ chType ] [ x0 ][ y0 ] > MaxTbSizeY )) | |     ( IntraSubPartitionsSplitType != ISP_NO_SPLIT &&     (subTuIndex < NumIntraSubPartitions − 1 | | !InferTuCbfLuma ) ) )   tu_y_coded_flag[ x0 ][ y0 ] ae(v)   if(IntraSubPartitionsSplitType !=ISP_NO_SPLIT )    InferTuCbfLuma = InferTuCbfLuma && !tu_y_coded_flag[x0 ][y0 ]  }

According to exemplary embodiments, the TU coded flag of aluma.component related semantics may also be shown as follows: atu_y_coded_flag[x0][y0] equal to 1 may specify that the luma transformblock contains one or more transform coefficient levels not equal to 0,and the array indices x0, y0 may specify the location (x0, y0) of thetop-left luma sample of the considered transform block relative to thetop-left luma sample of the picture, and when tu_y_coded_flag[x0][y0] isnot present, its value may be inferred as follows: if cu_sbt_flag isequal to 1 and one of the following (a), (b) conditions is true,tu_y_coded_flag[x0][y0] is inferred to be equal to 0 (a) subTuIndex isequal to 0 and cu_sbt_pos_flag may be equal to 1, (b) subTuIndex may beequal to 1 and cu_sbt_pos_flag may be equal to 0, otherwise, if treeTypeis equal to DUAL_TREE_CHROMA, tu_y_coded_flag[x0][y0] may be inferred tobe equal to 0, and further otherwise, tu_y_coded_flag[x0][y0] may beinferred to be equal to 1. In such syntax and related semantics, theremay not be a condition check about an ACT block for a TU coded flag.

Further, for an exemplary tu_y_coded_flag of an ACT block, the TU codedflag for a luminance component may be described as follows:

 if (!isChroma(partitioner.chType))  {   if (!CU::isIntra(cu) && trDepth== 0 && !chromaCbfs.sigChroma(area.chromaFormat))   {   TU::setCbfAtDepth(tu, COMPONENT_Y, trDepth, 1);   }   else if(cu.sbtInfo && tu.noResidual)   {    TU::setCbfAtDepth(tu, COMPONENT_Y,trDepth, 0);   }   else if (cu.sbtInfo &&!chromaCbfs.sigChroma(area.chromaFormat))   {    assert(!tu.noResidual);   TU::setCbfAtDepth(tu, COMPONENT_Y, trDepth, 1);   }   else   {   bool lumaCbfIsInferredACT = (cu.colorTransform && cu.predMode ==MODE_INTRA &&       trDepth == 0 &&!chromaCbfs.sigChroma(area.chromaFormat));    bool lastCbfIsInferred =lumaCbfIsInferredACT; // ISP and ACT are mutually exclusive    boolpreviousCbf  = false;    bool rootCbfSoFar  = false;    if (cu.ispMode)   {     ...    }    bool cbfY = lastCbfIsInferred ? true :     cbf_comp(cs, tu.Y( ), trDepth, previousCbf, cu.ispMode);   TU::setCbfAtDepth(tu, COMPONENT_Y, trDepth, (cbfY ? 1 : 0));   }  }

Accordingly, the TU coded flag of luminance may be inferred to 1 whenthe TU coded flag of chrominance channels are both zero and the currentCU is an intra block and is coded with ACT mode.

As described herein, there may be one or more hardware processor andcomputer components, such as buffers, arithmetic logic units, memoryinstructions, configured to determine or store predetermined deltavalues (differences) between ones of the values described hereinaccording to exemplary embodiments.

Accordingly, by exemplary embodiments described herein, the technicalproblems noted above may be advantageously improved upon by one or moreof these technical solutions. That is, according to embodiments, toaddress one or more different technical problems, this disclosuredescribes novel technical aspects in which an access unit delimiter(AUD) may be advantageously signaled to indicate which slice type valuesare present in the slices of the coded pictures in the access unitcontaining the access unit delimiter NAL unit. The pic_type may beuseful to identify whether the AU is independent or dependent from outerAU. Further, it is asserted that such novel syntax element signaling isadvantageous in indications of random access AU and robustness of AUboundary detection respectively according to exemplary embodiments andtherefore advantageous for improved accuracy and efficiency for example.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media or by a specifically configured one or morehardware processors. For example, FIG. 12 shows a computer system 1200suitable for implementing certain embodiments of the disclosed subjectmatter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 15 for computer system 1500 are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system 1500.

Computer system 1500 may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard 1501, mouse 1502, trackpad 1503, touch screen1510, joystick 1505, microphone 1506, scanner 1508, camera 1507.

Computer system 1500 may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen 1510, or joystick 1505, but there can also be tactilefeedback devices that do not serve as input devices), audio outputdevices (such as: speakers 1509, headphones (not depicted)), visualoutput devices (such as screens 1510 to include CRT screens, LCDscreens, plasma screens, OLED screens, each with or without touch-screeninput capability, each with or without tactile feedback capability-someof which may be capable to output two dimensional visual output or morethan three dimensional output through means such as stereographicoutput; virtual-reality glasses (not depicted), holographic displays andsmoke tanks (not depicted)), and printers (not depicted).

Computer system 1500 can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW1520 with CD/DVD 1511 or the like media, thumb-drive 1522, removablehard drive or solid state drive 1523, legacy magnetic media such as tapeand floppy disc (not depicted), specialized ROM/ASIC/PLD based devicessuch as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system 1500 can also include interface 1599 to one or morecommunication networks 1598. Networks 1598 can for example be wireless,wireline, optical. Networks 1598 can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks 1598 include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CANBus, and so forth. Certain networks 1598commonly require external network interface adapters that attached tocertain general-purpose data ports or peripheral buses (1550 and 1551)(such as, for example USB ports of the computer system 1500; others arecommonly integrated into the core of the computer system 1500 byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks 1598, computersystem 1500 can communicate with other entities. Such communication canbe uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbusto certain CANbus devices),or bi-directional, for example to other computer systems using local orwide area digital networks. Certain protocols and protocol stacks can beused on each of those networks and network interfaces as describedabove.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core 1540 of thecomputer system 1500.

The core 1540 can include one or more Central Processing Units (CPU)1541, Graphics Processing Units (GPU) 1542, a graphics adapter 1517,specialized programmable processing units in the form of FieldProgrammable Gate Areas (FPGA) 1543, hardware accelerators for certaintasks 1544, and so forth. These devices, along with Read-only memory(ROM) 1545, Random-access memory 1546, internal mass storage such asinternal non-user accessible hard drives, SSDs, and the like 1547, maybe connected through a system bus 1548. In some computer systems, thesystem bus 1548 can be accessible in the form of one or more physicalplugs to enable extensions by additional CPUs, GPU, and the like. Theperipheral devices can be attached either directly to the core's systembus 1548, or through a peripheral bus 1551. Architectures for aperipheral bus include PCI, USB, and the like.

CPUs 1541, GPUs 1542, FPGAs 1543, and accelerators 1544 can executecertain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM1545 or RAM 1546. Transitional data can be also be stored in RAM 1546,whereas permanent data can be stored for example, in the internal massstorage 1547. Fast storage and retrieval to any of the memory devicescan be enabled through the use of cache memory, that can be closelyassociated with one or more CPU 1541, GPU 1542, mass storage 1547, ROM1545, RAM 1546, and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture 1500, and specifically the core 1540 can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core 1540 that are of non-transitorynature, such as core-internal mass storage 1547 or ROM 1545. Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core 1540. A computer-readablemedium can include one or more memory devices or chips, according toparticular needs. The software can cause the core 1540 and specificallythe processors therein (including CPU, GPU, FPGA, and the like) toexecute particular processes or particular parts of particular processesdescribed herein, including defining data structures stored in RAM 1546and modifying such data structures according to the processes defined bythe software. In addition or as an alternative, the computer system canprovide functionality as a result of logic hardwired or otherwiseembodied in a circuit (for example: accelerator 1544), which can operatein place of or together with software to execute particular processes orparticular parts of particular processes described herein. Reference tosoftware can encompass logic, and vice versa, where appropriate.Reference to a computer-readable media can encompass a circuit (such asan integrated circuit (IC)) storing software for execution, a circuitembodying logic for execution, or both, where appropriate. The presentdisclosure encompasses any suitable combination of hardware andsoftware.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video coding performed by at leastone processor, the method comprising: obtaining a coding unit (CU) ofvideo data; determining whether to signal an adaptive color transform(ACT) flag based on both of values of a flag of the CU and a tree typeof the CU; and coding the video data based on a whether the ACT flag issignaled.
 2. The method according to claim 1, further comprising:determining whether the flag of the CU is set to a predetermined flagcondition; and determining whether the tree type of the CU is set to apredetermined tree type, and wherein determining whether to signal theACT flag is further based on whether the flag of the CU is set to thepredetermined flag condition and whether the tree type of the CU is setto the predetermined tree type.
 3. The method according to claim 2,wherein determining whether to signal the ACT flag is based on onlywhether the flag of the CU is set to the predetermined flag condition.4. The method according to claim 2, wherein the predetermined tree typeindicates a single tree type, and wherein the predetermined flagcondition comprises sps_act_enabled_flag being equal to
 1. 5. The methodaccording to claim 1, wherein determining whether to signal the ACT flagis implemented regardless of whether a prediction mode of the CU is anintra mode.
 6. The method according to claim 1, further comprisesdetermining whether transform unit (TU) coded flags are both zero andwhether the CU is coded with an ACT mode.
 7. The method according toclaim 6, wherein the TU coded flags are flags of chrominance channels.8. The method according to claim 7, further comprising: determining a TUcoded flag of luminance is to be inferred to be 1 based on determiningthat the TU coded flags are both zero and that the CU is coded with theACT mode.
 9. The method according to claim 8, wherein determining the TUcoded flag of luminance is to be inferred to be 1 is implementedregardless of whether a prediction mode of the CU is an intra mode. 10.The method according to claim 9, wherein coding the video data isfurther based on determining whether the TU coded flag of luminance isto be inferred to be
 1. 11. An apparatus for video coding, the apparatuscomprising: at least one memory configured to store computer programcode; at least one processor configured to access the computer programcode and operate as instructed by the computer program code, thecomputer program code including: obtaining code configured to cause theat least one processor to obtain a coding unit (CU) of video data;determining code configured to cause the at least one processor todetermine whether to signal an adaptive color transform (ACT) flag basedon both of values of a flag of the CU and a tree type of the CU; andcoding code configured to cause the at least one processor to code thevideo data based on a whether the ACT flag is signaled.
 12. Theapparatus according to claim 11, wherein the determining code is furtherconfigured to cause the at least one processor to determine: whether theflag of the CU is set to a predetermined flag condition; whether thetree type of the CU is set to a predetermined tree type; and whether tosignal the ACT flag is further based on whether the flag of the CU isset to the predetermined flag condition and whether the tree type of theCU is set to the predetermined tree type.
 13. The apparatus according toclaim 12, wherein determining whether to signal the ACT flag is based ononly whether the flag of the CU is set to the predetermined flagcondition.
 14. The apparatus according to claim 12, wherein thepredetermined tree type indicates a single tree type, and wherein thepredetermined flag condition comprises sps_act_enabled_flag being equalto
 1. 15. The apparatus according to claim 11, wherein determiningwhether to signal the ACT flag is implemented regardless of whether aprediction mode of the CU is an intra mode.
 16. The apparatus accordingto claim 11, further comprising second determining code configured tocause the at least one processor to determine whether transform unit(TU) coded flags are both zero and whether the CU is coded with an ACTmode.
 17. The apparatus according to claim 16, wherein the TU codedflags are flags of chrominance channels.
 18. The apparatus according toclaim 17, further comprising: third determining code configured to causethe at least one processor to determine whether a TU coded flag ofluminance is to be inferred to be 1 based on determining that the TUcoded flags are both zero and that the CU is coded with the ACT mode.19. The apparatus according to claim 18, wherein determining the TUcoded flag of luminance is to be inferred to be 1 is implementedregardless of whether a prediction mode of the CU is an intra mode. 20.A non-transitory computer readable medium storing a program causing acomputer to execute a process, the process comprising: obtaining acoding unit (CU) of video data; determining whether to signal anadaptive color transform (ACT) flag based on both of values of a flag ofthe CU and a tree type of the CU; and coding the video data based on awhether the ACT flag is signaled.